The invention relates to a method for calibrating flow meters for fluid media and a calibration device, which is suitable in particular for carrying out such a method.
Flow meters are used for determining the flow rate of a fluid medium, for example, diesel oil, and are typically adjusted and/or calibrated by means of a defined volume stream. Nevertheless, measurement errors and/or measurement uncertainties result in the conventional calibration methods, which are substantially to be attributed to the fact that physical effects of different types, which occur at higher temperatures, are not taken into consideration. Thus, upon heating of the fluid medium, increasing measured value scattering occurs in such a flow meter due to the mixing of gas bubbles and fluid then resulting as a consequence of the heating and the rising system pressure accompanying this, wherein the viscosity of the fluid medium decreases with rising fluid temperature, which results in a successively decreasing friction resistance of the fluid medium on surfaces of mechanically moving components of such a flow meter. In particular at higher temperatures, such flow meters are thus no longer reliably usable, because the required tolerances are exceeded as a result of systematic drifting of the flow measured values of the flow meter. Such measurement deviations are not detectable using conventional calibration methods, however, because the applicable calibration standard guidelines for carrying out calibrations only prescribe a calibration temperature of 40° C.